Practical ship afterbody optimization by multifidelity techniques

Abstract

ABSTRACT This paper discusses multifidelity methods for CFD-based optimization of ship afterbody designs; aimed at a fast application to a variety of practical cases. Surrogate-based global optimization is used, using a multi-objective genetic algorithm. The surrogates are derived by combining few high-fidelity computations, by free-surface RANS codes, with many low-fidelity computations. For rather slender vessels for which the wave resistance variations over the design space are dominant, a free-surface potential flow code is found very effective as a low-fidelity solver, permitting a large reduction of the number of RANS computations and the associated cost. Examples are shown for model 5415 and a fast displacement vessel. For cases with variation in both viscous and wave resistance, an alternative method is used combining coarse and fine-grid RANS computations; the coarse-grid ones being about 20 times cheaper. Application of this coarse/fine grid multifidelity optimization to a containership and a motor yacht shows its effectivity.